microbenchmark compaction

Comparing ./db_basic_bench_main to ./db_basic_bench_new
Benchmark                                                                                                                                                          Time             CPU      Time Old      Time New       CPU Old       CPU New
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
ManualCompaction/comp_style:0/max_data:33554432/per_key_size:256/enable_statistics:0/iterations:1                                                               +0.0014         +0.0162     104328093     104470603      83025631      84374645
ManualCompaction/comp_style:0/max_data:33554432/per_key_size:256/enable_statistics:1/iterations:1                                                               +0.0613         +0.0488     103397520     109737940      83940460      88033800
ManualCompaction/comp_style:0/max_data:33554432/per_key_size:1024/enable_statistics:0/iterations:1                                                              +0.0511         +0.0540      70115625      73700485      49763647      52452408
ManualCompaction/comp_style:0/max_data:33554432/per_key_size:1024/enable_statistics:1/iterations:1                                                              +0.0728         +0.0704      70247399      75363638      50405396      53953193
ManualCompaction/comp_style:0/max_data:134217728/per_key_size:256/enable_statistics:0/iterations:1                                                              +0.0158         +0.0547     433138116     439984859     367486862     387605709
ManualCompaction/comp_style:0/max_data:134217728/per_key_size:256/enable_statistics:1/iterations:1                                                              +0.0178         +0.0304     444137895     452023186     383545330     395206423
ManualCompaction/comp_style:0/max_data:134217728/per_key_size:1024/enable_statistics:0/iterations:1                                                             +0.0387         +0.0527     272288936     282821622     219063595     230605430
ManualCompaction/comp_style:0/max_data:134217728/per_key_size:1024/enable_statistics:1/iterations:1                                                             +0.0161         +0.0400     289351315     294001296     230345911     239568110
ManualCompaction/comp_style:1/max_data:33554432/per_key_size:256/enable_statistics:0/iterations:1                                                               +0.0516         +0.0476     101769660     107017587      82359754      86276611
ManualCompaction/comp_style:1/max_data:33554432/per_key_size:256/enable_statistics:1/iterations:1                                                               +0.0099         +0.0486     107374165     108439457      83940699      88024188
ManualCompaction/comp_style:1/max_data:33554432/per_key_size:1024/enable_statistics:0/iterations:1                                                              +0.0727         +0.0510      68380281      73353244      50150511      52705880
ManualCompaction/comp_style:1/max_data:33554432/per_key_size:1024/enable_statistics:1/iterations:1                                                              +0.0549         +0.0704      72071041      76026755      51525695      55154139
ManualCompaction/comp_style:1/max_data:134217728/per_key_size:256/enable_statistics:0/iterations:1                                                              +0.0001         +0.0346     438410258     438440634     371114630     383967068
ManualCompaction/comp_style:1/max_data:134217728/per_key_size:256/enable_statistics:1/iterations:1                                                              +0.0138         +0.0446     443967105     450094523     381052071     398044490
ManualCompaction/comp_style:1/max_data:134217728/per_key_size:1024/enable_statistics:0/iterations:1                                                             +0.0255         +0.0563     274808133     281815736     217573284     229825656
ManualCompaction/comp_style:1/max_data:134217728/per_key_size:1024/enable_statistics:1/iterations:1                                                             +0.0258         +0.0514     284587856     291937100     228774804     240533312